Don't use admin cert during KRA installation
    
    KRA installation currently imports the admin cert.  FreeIPA does not
    track this cert and it may be expired, causing installation to fail.
    Do not import the existing admin cert, and discard the new admin
    cert that gets created during KRA installation.
    
    Part of: https://pagure.io/freeipa/issue/7287
    
    Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>